1. Field of the Invention
The present concept relates to rotary compressors. More particularly, the present concept relates to discharge valves for rotary compressors.
2. Description of the Related Art
A typical rotary compressor includes a housing, a stator positioned within the housing, and a rotor driven, i.e., rotated, by the stator, the rotor being mounted to a first end of a crankshaft. The compressor further includes a compression mechanism operably engaged with the opposite end of the crankshaft. The compression mechanism typically includes an eccentric member engaged with the crankshaft that is rotated within a stationary cylinder block to compress a working fluid, or refrigerant, in a compression chamber defined by the eccentric member and the stationary cylinder block. Commonly, a discharge valve is mounted to the stationary cylinder block to release pressurized refrigerant from the compression chamber.
In rotary compressors of the general type disclosed in the present application, unlike the typical compressors described above, the compressor includes a rotatable rotor that surrounds the eccentric member. Such compressors are illustrated and described in co-pending U.S. Published Application No. 2005/0201884 entitled COMPACT ROTARY COMPRESSOR WITH CARBON DIOXIDE AS WORKING FLUID, filed on Mar. 9, 2004. In these compressors, the refrigerant is drawn into a compression chamber defined by the rotor and the eccentric member and is compressed by the relative movement thereof. As the rotating rotor defines the compression chamber, these compressors do not have a stationary cylinder block and the discharge valve is typically mounted on the rotor.
A discharge valve typically includes a valve member that is yieldably positioned against a discharge port of the compression chamber to permit refrigerant to be drawn into the compression chamber and compressed therein. In some embodiments, the valve member, or valve head, is held in this position by a valve spring until sufficient fluid pressure has been generated within the compression chamber. Subsequently, the pressurized fluid lifts the valve head away from the discharge port allowing fluid to be discharged. After a quantity of working fluid has been discharged from the compression chamber, the fluid pressure inside the compression chamber decreases, the pressure force acting on the valve head decreases, and the valve spring repositions the valve head against the discharge port.
The discharge valve, in compressors of the general type disclosed in the present application, may be oriented such that the valve head, when it is displaced, is displaced in a generally radial manner with respect to the axis of rotation of the rotor. As a result of orienting the valve in this manner, the valve head, when the rotor is rotated, is biased radially outwardly towards its open position by an acceleration acting radially on the valve head. To compensate for this acceleration, the stiffness of the valve spring holding the valve head in place can be selected such that valve head remains seated until it is displaced by the fluid in the compression chamber once the fluid has reached a pre-determined pressure level.
However, the valve head may also experience an acceleration, and force, tangential to the radial direction discussed above. This tangential force can be created by gas drag, changes in angular velocity of the rotor, or changes in radial position of the valve head. A tangential force created by a change in the radial position of the valve head occurs when the valve head is displaced from the valve seat to release pressurized refrigerant from the compression chamber, and also when the valve head is returned to the valve seat. This tangential force may cause the valve head to displace tangentially with respect to the desired radial path. In effect, the tangential force acting on the valve head may displace the valve head in a non-radial direction or along a curvilinear path, for example. As a result, the valve head may become misaligned with respect to the valve seat, thus allowing semi-compressed working fluid to escape through the compression chamber discharge port prematurely. What is needed is an improvement over the foregoing.